1. Field of the Invention
The present invention relates to watercraft, such as surfboards and surf skis, and particularly relates to fins on watercraft.
2. Description of the Background Art
Water craft such as surfboards, surf skis and wind surfers for example, are provided with one or more fins at their underside for stability and to allow a rider better control of direction and manoeuvrability. Many riders prefer certain fin profiles for particular conditions or riding styles so that it has become commonplace to provide such craft with slots capable of accepting interchangeable fins.
The designs of watercraft and specifically surfboards have advanced to include multi-fin systems. The first fin system was a single center fin to enable the basic maneuvering of the board. Developments in the 1980s resulted in the addition of side fins, either as a 3 (tri) fin system comprising a center fin and 2 side fins, or just two side fins (twin). Differing board performance can be achieved by extending the number of fins to 4 fins (quad) that is 2 sets of fins per side.
Of these combinations the one that provides the maximum flexibility is the 5 fin box system, as illustrated in FIG. 13, in that it combines the quad and the tri fin setups. This enables the user to use a standard tri fin set up of a center and a side fin each side, or the alternative of removing the center fin and adding two trailing rear side fins behind the existing side fins of the tri setup to create the quad.
For the tri side fins to provide the required steering characteristics, the inside face of the fin blade is generally flat or has a concave profile. The design of the trailing rear side fins in a 4 fin configuration, differ to the tri side fins, being generally smaller, can be symmetrical double foiled fins, enabling their use in either center or rear side trailing fin positions.
Another characteristic of the trailing rear side fins is that they are generally canted at a smaller angle (typically 2 degrees) than those of the tri Side fins (6 degrees). The fin placement for the tri configuration is well known by the industry, however, when the center fin of the tri configuration is removed and replaced by the two trailing side fins of the quad configuration the relative distance between the two sets of side fins needs to be adjusted for optimum performance.
It would be an advantage to the industry if a standard double foiled symmetrical axial aligned fin with a fin tab arrangement shorter than the length of the fin box slot, containing elongated dual-sided screw receiving slots, enabling the variable adjustment of the fin can be used along with a standard fin box that can be installed at a variable cant angle enabling a single fin and fin box to be used in multiple positions on the board at the time of manufacture.
Another feature particularly of high performance surf boards is that the underside surface of the board is provided with scalloped channels between the center fin and the side fins. These concave formations can cause the edges of the flanges of the fin boxes to protrude through the fiberglass surface of the underside surface of the board.
The present applicant disclosed in WO2006/077470 arrangements of fin boxes adapted to accept a variety of proprietary fin tab configurations.
One problem with fin boxes adapted to accept various fin tab configurations is that the length of slot required is such that distortion of the box may occur when heavy lateral loads are applied to large fins, or when the side retention screws are over tightened. This distortion takes the form of a spreading of the side walls of the slot.
To ensure waterproofing and increased structural strength of the fin box bond to the watercraft core it is preferred to have a layer of re-inforcing cloth to cover the external section of the outer surface of the fin box, and for sections of that surface to be perforated or grooved, to improve the resin bond to the fin box.
A disadvantage with the fixing of a fin box into the core of a water craft is that in some fin box installations a cavity is cut through the outer glassed surface of the board. This causes some inherent weakness as there is no direct bond between the fin box and the glassed surface.
A common feature of systems which provide for interchangeable fins to be retained within a fin box is the securing of the fin tab in the fin box by means of one or more grub screws. Such screws are generally provided with a hexagon drive socket at one end and threaded for their entire length. A problem with this arrangement is that it is easy for a user, anxious not to lose a fin from the box, to over-drive the screw with the associated risk of damage to the fin tab and/or the fin box, or even of stripping the thread of the screw hole within the fin box.
The fin box disclosed herein addresses or at least ameliorates all or some of the above disadvantages.
The term “comprising” (and grammatical variations thereof) is used in this specification in the inclusive sense of “having” or “including”, and not in the exclusive sense of “consisting only of”.
The above discussion of the prior art in the Background of the invention, is not an admission that any information discussed therein is citable prior art or part of the common general knowledge of persons skilled in the art in any country.
In this specification, terms such as upper, under, lower and vertical etc. refer to surfaces and directions when a water craft is oriented for use with its median plane substantially horizontal.